Photoelectric cell



July 17, 1928.

V. K. ZWORYKIN PHOTOELECTRIC CELL Filed .July 13 1925 2 sheets-sheet 2 Patented July 1 7, 1928.

UNITED STATES PATENT OFFICE.

VLADIMIR K. Z'WORYKIN, 0F WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WEST- INGHOUSE ELECTRIC MANUFACTURING COMPANY, CORPORATION 0F PENNSYL- VANIA.

PHOTOELECTBIC CELL'.

Application led July 13, 1925. Serial No. 43,220.

My invention relates, in general, to photoelectric cells.

One object of'm invention is to increase the sensitiveness o photoelectric cells of the alkali t e.

Aiiot er object of my invention is to greatly increase the amount of current that ma be obtained from a hotoelectric cell.

nother object of m invention is to provide a thermionics tu e that may be controlled by light. A

Another object of my invention is to provide a control electrode that is sensitive to li lit to effect the control of a thermionic tu e.

A still further object of my inventionis to provide a plurality of electrodes, one of which is light-controlled, for controlling a thermionic tube.

There are other objects of my invention which,.together with the foregoing, will be described in the following detailed specification.

In practicing my invention,'I may employ a thermionic tube constructed in avmanner substantially similar to the thermionic tubes employed as radio detectors and amplifiers, and commonly known las an audion. That is, a tube having a hot cathode, a grid and a cold anode. The construction, of course, may be modified in order to carry out my invention, as will appear subsequently.

Referring now to the drawings,

Figure 1 is a cross-sectional view of a preferred form of my photoelectric cell, and a diagrammatic view of associated circuits and apparatus.

Fig. 2 is a sectional view of a fragmentary portion of the photoelectric cell Ishown in Fig. 1, and

Fig. 3 is a view similar to Fig. 1, ofa modified form of photoelectric cell wherein the output of the device is materially greater than that shown in Fig. 1.

Referring now to Fig. 1, I will describe the mannerl in which my improved photoelectric cell is constructed. A glass bulb 1, of a shape such as shown in Fig. 1, is first treated so that a deposit 2 of conducting ma terial may be formed `on the lower inner portion thereof. This deposit 2 may be of platinum, or any other suitable material,

lthe foregoing process, the step which inand is deposited from a solution or in any well known manner.

a grid 4 and an anode or plate 5. The grid 4 is somewhat modified from the usual grid employed in thermionic tubes b being of finermesh and by having a solidy cap 6 and a solid ortion 7. The portion 7 ismttached to a g ass mounting or press 9 which is sealed in the bulb 1. The deposit is, of course, present on the glass mounting 9 and an electrical connection is thus made between the grid 4 and the deposit 2. Connections to the cathode 3 are made in the usual way through the press 9.

The anode 5 is'supported by a glass press 10 which is also sealed in a lateral extension of the bulb 1. The connection from the anode 5 is taken through the press 10. `The anode 5 may be slightly cone-shaped as shown. The solid portions 6 and 7 of the grid 4 are provided or the purpose of shielding the ight .emitted from the hot cathode 3 from reaching any portion of the inner surface of the bulb 1. A photoelectric element, such as potassium, caesium or sodium, isthen deposited on` the metallic surface 2 in the manner shown at 12.

Assuming that potassium'is the element that has been employed for makin this deposit, hydrogen will then be passe through the bulb .1, and connections will be made so that electric.. discharge occurs between the anode 5 and the grid 4, the grid circuit comprising the deposit 2. The resulting chemical action between the hydrogen and the potassium causes a film of potassium hydride to be formed in a colloidal state ony the potassium. The potassium hydride is highly `active photoelectrically, that is it emits electrons under the influence of light.

The manner oftreatment outlined above, by which a deposit of potassium hydride is placed on the metallic deposit in a colloidal form, renders the rate at which the electrons are emitted from ten to twenty times greater than if it were treated by other known means.

The hydrogen is then pumped from the bulb 1 and the bulb is evacuated by any well -1 known means.

It will be understood, of course, that in volves the `deposit of the photoelectric ele meut on the metallic deposit is accomplished as quickly as possible in order that the various elements inside the bulb 1 will not be short-circuited. v

In order to describe the Operation of the photoelectric cell, itwill be understood that the filament or cathode 3 is connected through a variable resistor 15 to a battery 16. and the plate or anode 5 is connected to the filament throuvh abattery 17. When the photoelectric cell is dark and current 1s passed through the filament 3, the latter becomes active and electrons are emitted. These electrons collect on the grid 4 and impart a negative charge to it. This places a negative potential on the grid 4 and the photoelectric material 12. lThe negative charge builds u to such degree that the electrons'from t e filament 3 are prevented from reaching the anode 5 by means of the space charge which is controlled by the accumulated negative charge on the.grid 4.`

The negative charge on the grid 4 necessary to prevent the electrons from reaching the anode 5 varies with the distance between the electrodes and with the mesh of the grid. There is, thus, no current flow from the filament 3 to the anode 5.

Vhen the photoelectricv cell is illuminated, the photoelectric material 12 vimmediately becomes active to emit electrons, with the consequence that the negative potential of the photoelectric material becomes less. As this photoelectric material is con nected to the id 4, the negative charge on the grid is 4re uced, and the space charge is no longer effective to prevent the electrons emitted from the filament 3 reaching the anode 5. The electrons from the filament 3 are thus permitted to flow to the anode 5. The current in the plate circuit may then operate a. relay 18, depending on the rate at which the electrons are emltted from the photoelect-ric material 12. The relayT 18 may control an electrical circuit in any desired manner. s

It will be seen that the number of electrons which are permitted to flow to the anode 5 from the cathode 3 depends upon the space charge which is controlled by the grid 4. The charge on the grid 4 is, in turn, dependent upon the amount of light reaching the photoelectric material 12. By this means, a thermio'nic current of considerable magnitude is secured. This thermionic current is proportional to the amount of light falling upon the photoelectric cell. By the use of my construction, it is possible to obtain a thermiouic current several thousand times secure from a photoelectric cell of the alkali type wherein the electrons emitted control the amount of current directl In the present case, the electrons emitte from the ond batter eater than the current that can be navigare light act in the manner of a relay to control .a larger current-giving source.

Another preferred form of vmy invention is shown in Fig. 3. vThe photoelectric cell' shown in Fig. 3, is constructed in a manner substantially similar to that of the photoelectric cell shown in Fig. 1, previously described. The main difference is that a second grid is provided between the filament and the anode. That is, the bulb 21 may be first coated on the inside lower portion with a metallic deposit 22.

The usual elements of a thermionic tube are then place in the bulb in a well known.v

manner. These elements comprise a filament 23, a grid 24, a second grid 25 and a pla-te or anode 26. The first grid 24 may be constructed in the same manner as the grid employed in the usual 'thermionic tubes well known in the radio art. The second grid 25 is slightly modified, inasmuch as it 'is of finer mesh andis provided with a solid cap 27 and a solid portion 28. The solid portion 28 is attached to the glass mounting 30 in such manner that a connection is made between "the metallic deposit and the second grid 25. I The cap 27 and the solid -portion 28 of the second grid 25 are soconstructed that no light from the filament 23 will reach the inside of the bulb 1. The anode 26 is supported by a glass mounting 29 in the usual manner. The outer 3 electrodes are .mounted coaxially about the cathode.

Potassium may be then distilled' upon the metallic surface on the inside of thebulb 21 and treated'with hydrogen to 'form a film of -potassium hydride in a colloidal state, in the same manner as before described. In addition, vthe hydrogen is pumped out and replaced with an inertas atmosphere at a pressure which will give maximum response of thematerial. AWhen the tube is rst made, a contact member 31 is placed therein for electrical connection to the metallic and photoelectric deposits.

In order to describe the operation of the photoelectric cell of Fig. 3, it will be under-l The terminal 31 is connected through a re sistor 36, high-potential battery 37 and sec- 34 to the anode 26. The voltage of the attery 37 ma'be of the order of several hundred volts. e resistance of the resistor 36 may be of the order of 50 megohms.

hotoelectric x stood that certain electrical connections are y It willfbe seen that the negative terminal Y photoelectric materlal under the mfluence of .of the battery 37 is connected to the terminal 13o 31 and that the positive pole of the battery 34 is connected to the anode 26. Inasmuch as the voltage of the batteries 34 and 37 are added together, a high negative potential is placed upon the metallic deposit 22 with respect to the anode 26. A low positive potential from the battery 34 is also placed upon the grid 24. v v It will first be assumed that the photoelectric cell is dark. When the current is passed through the filament or cathode 23, electrons are emitted from the filament. These electrons do not How to the grid 24 because of the fact that there is a high negative potential existing upon the second grid 25 from the battery 37. Consequently, there is no current flow in the circuit including the relay 35. When the photoelectric cell is illuminated, the photoelectric material begins to emit electrons, the number of which is proportional to the intensity of light. These electrons fiow from the photoelectric material to the anode 26 under the influence of the voltage impressed by the batteries 37 and 34 in series. v

Immediately upon the iow of current there is a voltage drop across the resistor 36, and the voltage on the grid 25 is reduced to such an extent that the space charge is not effective to prevent the electrons emitted from the cathode 23 reaching the grid 24.

\ The voltage drop is proportional to the electron flow from the photoelectric material. This, in turn, is proportional to the intensity of light on the photoelectric cell. The voltage drop regulates the space charge which, in turn, controls the number of electrons that reach the grid 24. The electrons reaching the grid 24 thus cause the current to iiow through the circuit including the relay 35. The amount of current is relatively high. In fact, the only limit to the amount ofeurrent that may be obtained is the amount of heat radiated by the filament which evaporates the potassium. .By proper cooling arrangement, a very large current output may be secured'.V In my experiments, where no special provisions were made to secure better heat radiation, I have obtained a current as high as 60 milliamperes. This current is effective to operate the relay 35 to perform any desired function.

When the photoelectric cell is darkened, the photoelectric substance does not emit electrons and there is no current flow from the photoelectric material to the anode 27. Consequently, there is no voltage drop across the resistor 36, and a' high negative potential is placed on the grid 25 which controls the space charge so that no electrons from the cathode 23 reach the grid 24.

My invention is not limited to the particular arrangement of the appara-tus described, but may be variously modified without departing from the spirit and scope thereof, as set forth in the appended claims.

I claim as my invention:

l. In a photo-electric device, an evacuated envelope, a cathode and an anode'mounted therein, two control electrodes mounted'between said cathode a-nd anode and .a coating of conductive photo-sensitive material eX- tending into electrical connection with the control electrode nearer theanode.

2. In a photo-electric device, an evacuated envelope having a press and an inwardly projecting skirt surrounding said press, a cathode mounted on said press within the envelope, a control electrode mounted on said skirt within said envelope, a conductive photo-sensitive material coating and a portion of the inner surface of said envelope and the surface of said skirt farthest from said press and a conductive connection between said coating and the` control electrode.

3. In a photo-electric device, an evacuated envelope having a press and an inwardly projecting skirt surrounding said press, a cathode and a control electrode mounted on said press within the envelope, a second control electrode mounted' on said skirt within said envelope, a conductive' photo-sensitive material coating and a portion of the inner surface of said envelope and the surface of said skirt farthest from said press and a conductive connection between said coating and the second control electrode.

4. In a photo-electric device, an evacuated envelope having a press and an inwardly projecting skirt surrounding said press, a cathode and a control electrode mounted on said' press within the envelope, a second control electrode mounted on said skirt within said envelope, a conductive photo-sensitive material coating and a portion of the inner surface of said envelope and the surface of said skirt farthest from said press, a conductive connection between said coating and the second control electrode, a second press and an anode supported thereby.

' In testimony whereof, I have hereunto subscribed my name this 1st day of July,

VLADIMIR K. ZWORYKIN.

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